A photocatalyst-plasma hybrid air purification system that is used for decomposing pollutants in air to purify the air is known in the art. In this photocatalyst-plasma hybrid air purification system, in addition to decomposing the pollutants by the action of plasma at the room temperature and atmospheric pressure, the pollutants are decomposed by a photocatalytic action by exciting titanium oxide, which is a photocatalyst, by plasma emission.
FIG. 21 depicts such a photocatalyst-plasma hybrid air purification system 41. The photocatalyst-plasma hybrid air purification system 41 includes an inner cylindrical electrode 42 and an outer cylindrical electrode 43 with an air space therebetween. A photocatalytic layer is provided on an inner surface of the outer cylindrical electrode 43. The inner cylindrical electrode 42 and the outer cylindrical electrode 43 function as a pair of plasma generation electrodes. Such a photocatalyst-plasma hybrid air purification system is disclosed, for example, in Japanese Patent Application Laid-open No. 2001-187319.
In the conventional photocatalyst-plasma hybrid air purification system, even if a large amount of photocatalytic particles are mixed in the photocatalytic layer, because the air comes in contact only with a surface of the photocatalytic layer, air purification capacity is low. Moreover, due to the position of the photocatalytic layer on the inner surface of the outer cylindrical electrode 43, it is not easy to increase a surface area of the photocatalytic layer, i.e., it is not easy to increase the air purification capacity.
Furthermore, the space between the inner cylindrical electrode 42 and the outer cylindrical electrode 43 cannot be widened; because, if the space is widened, the air that needs to be purified will not efficiently contact the photocatalyst. Because the space is narrow, it is not possible to pass a lot of air through this space.
An air purification system that solves the above problems is disclosed in Japanese Patent Application Laid-open No. H11-47558. As shown in FIG. 22, this air purification system has a wire-shaped high voltage electrode 52 arranged in an insulating cylinder 51 that constitutes an air passage. A grounding electrode 53 is arranged on an outer periphery of the insulating cylinder 51. A photocatalyst member 55 formed by winding a porous photocatalyst sheet 54 is arranged between the high voltage electrode 52 and the grounding electrode 53 while securing an electric discharge space.
The porous photocatalyst sheet 54 is formed in the following manner. A dispersion of anatase titanium dioxide or fluorinated resin, which is a photocatalyst, is applied to a sheet-like porous substrate and dried, or the sheet-like substrate is dipped in the dispersion, and removed from the dispersion and dried. This results in the formation of a film of photocatalyst on the substrate. The substrate can be a nonwoven cloth (a felt) made from glass fiber, ceramic fiber, metallic fiber, and carbon fiber.